Method and apparatus for conditioning mineral aggregate



H. M. STAFFORD METHOD AND APPARATUS FOR CONDITIONING MINERAL AGGREGATE May 19, 1936.

Original Filed March '7, 1932 1 are? Patented May 19, 1936 UNITED STATES LPATETNTG OFFICE METHOD AND ALPAEATUS FOR CONDI TIONING MINERAL AGGREGATE Hiram M.

mesne assignments,

Stafford, Chicago, Ill.,"assignor, by to Sealdrok Company of March 7, 1932. This Serial No. 20,683

application May 9, 1935,

8 Claims. ((31. 94-43) My invention relates to a method and app ratus for conditioning crushed stone, or mineral aggregate in general, and to the product formed thereby, at the quarry or other source of supply,

and more particularly to a style of treatment which enables the aggregate to be used immediately or stored for any length of time, or subsequently reprocessed to meet the particular specifications for road building, street paving, miscel- 10 laneous surfacing, and various otherconstruction purposes.

One object of my invention is to devise a method of the character indicated wherein the aggregate is first thoroughly dried by heating, after which the individual pieces, while in this heated, dried and expanded condition, are impregnated and fully coated with a hydrocarbon or bituminous solution at a relatively lower temperature,

such as an asphalt base ,oil, which not onlywaterproofs and hermetically seals each piece, but also provides a coat that will efiiciently bond with similar coats on other pieces, or with other paving substances when the aggregate is substantially reprocessed to make a complete paving material. A further object is to devise a conditioning method which provides for a substantial looking or keying of the waterproof coating with the interstices or pores of each piece of the aggregate, so that the coating is characterized by" toughness and a capacity for remaining in place on the surface of each piece, regardless of any abrasion due to handling, or the deteriorating effects of climatic changes.

A further object is to devise a method in which the temperatureoi the aggregate is sufiiciently reduced after drying to obviate any possibility of a distillation-of the lighter fractions of the hydrocarbon solution when applied to the aggregate, the properties of these solutions being fully pre- 0 served in order that it may fulfill its primary function with respect to the aggregate.

A further object is the inclusion in the method, as above set forth, of the step of applying the hydrocarbon to the aggregate, which is accom- 45 plished by spraying the pieces of the aggregate while substantially suspended in, or otherwise directed through, a suitable chamber.

A further object is the provision of a conditioning method which is continuous in operation, enabling the crushed stone to be deposited in a dryer at one end of the line and the fully coated and water-proofed pieces to be delivered from a coating chamber at the opposite end directly into 55 suitable receptacles.

A further object is the devising of apparatus for the carrying out of the above method, involving the use of a dryer, an intervening storage bin, and a coating or waterproofing chamber having spray nozzles and suitable agitating or stirring devices for insuring the thorough coating of each piece, the bin being utilized to regulate the flow of aggregatethrough the coating chamber.

A further object is to devise a novel form of dryer, operating on the counterflow principle, in which heat is applied to the aggregate during a portion of its passage through the-dryer and cooled to a predetermined extent during its remaining movement in the dryer by air which is thereafter utilized to remove the moisture that has been evaporated from the aggregate.

A further object is to devise an article of manufacture in the form of mineral aggregate pieces which are substantially devoid of moisture and air and in which the individual pieces are coated with a thin bituminous covering which extends into and is interlocked in the interstices of the pieces for the purpose of hermetically sealing the pieces against subsequent moisture absorption, the coating being such as to prevent the coalescing of the pieces together into an agglomerated form when stock piled for an appreciable length of time, but fusing and merg n with a subsequently added bituminous coating in the making of roadway material, for example, wherein the coating on the pieces is substantially uniform in consistency and keyed and interlocked in the pores of the pieces.

7 The most important material in any bitmninous type of paving or road-building mixture is the mineral aggregate, since primary dependence is placed thereon, not only to sustain the load and ravages of traffic, but also to withstand the expansive and contractive stresses and strains due to climatic changes. It is therefore highly desirable that the aggregate be efliciently treated in order to avoid an inferior roadway. In general, two methods are, now employed in the handling of material intended for bituminous road building. The materials, such as crushed stone, asphalt cement and the like. are either assembled at the point of use and then mixed in temporary plants composed of inadequate equipment where dryers are not available, or they are delivered to a special type of plant, which is a short distance from the construction point, for treatment, mixing and use immediately in the building of a road in order to prevent any hardening of the composing material. Both of these methods are 55 characterized by certain inherent disadvantages as willnow be discussed.

The principal objection to the firstmethod is that it is impossible to secure an effective and lasting coating of the crushed stone with a bituminous substance, because of moisture andair which is held within the interstices and on'the surface of the stone pieces. The moisture presents what might be called an insulating layer or film that either prevents the bituminous substance from eifectively adhering to the surface of the stone in the first instance, or if some degree of adherence is obtained, the coating is sub sequently removed during cold weather by the expansion of the moisture within the stone by freezing, while the contained air prevents the bituminous substance from entering the interstices of the stone and making a firm interlock therewith.

The practice of the second method is inherently limited by two factors, namely, the necessity for having expensive and intricate equipment for the heating of the stone in order to drive the moisture off, these plants usually being located in urban localities only and therefore not accessible over wide ranges of country districts, and also because of the necessity for utilizing the paving material formed in these machines-within a relatively short time after its production; otherwise, the aggregate pieces become so thoroughly bonded together that they cannot be handled.

According to my invention, it is proposed to condition the mineral aggregate at the quarry or other source of supply in such a manner that it may be used as produced. or at any time thereafter be processed according to any of the simple methods now in use and with inexpensive equip ment forthe purpose of forming a complete paving material. In general, the practice of this invention is not intended to result in the production of a complete, bituminous paving material, as this term is generally understood, but ordinarily relates to the conditioning of the aggregate portion thereof in order that it will combine more efiectively with other bituminous substances to provide a paving that will be characterized by greater resistance to wear and weather. However, it is contemplated that aggregate, conditioned according to this method may be used immediately for stone macadam roads, or for other construction purposes.

Since the contained moisture and air presents the principal problem in the proper handling of aggregate intended for paving purposes, the present invention contemplates their removal and the subsequent treatment of the stone to hermetically seal its pores so that moisture can never thereafter penetrate into the interstices of the stone, nor adhere to any marked extent on the surface. Briefly, this result is effected by applying a waterproof coating to the pieces of stone, which additionally has the property of fusing or-merging with the bituminous material which may thereafter be mixed with the coated stone in order to produce a complete paving substance.

In carrying out my invention, the mineral aggregate is dried by heating and thereafter, while still warm, but at a somewhat lower temperature, is subjected-to the application of a relatively cool, hydrocarbon or bituminous solution which impregnates and thoroughly coats the individual pieces, the temperature of the latter preferably being such as to prevent any distillation of the latter constituents of the solution. The extent of the impregnation will depend not only upon the size of the aggregate pieces, but also upon their degree of porosity. Specifically, the drying of the aggregate accomplishes an enlargement of the pores of the stone, a removal of the contained moisture and a portion of the contained air. Owing to the dried and expanded condition of 'each stone piece, it will be obvious that the sudden cooling and contraction thereof will effect a penetration of each piece to some depth by the solution, so that the latter, in addition to adhering in the customarymanner to the surface of the stone pieces, will also be substantially keyed or locked in the interstices thereof. The coat ing so applied is in the nature of a waterproof film which hermetically seals the interstices of each piece and absolutely prevents the absorption thereafter of any moisture by the stone.

The-mineral aggregate which is conditioned according to this method may be used at once, or held in stock piles for any desired length of time, and may be shipped over any distance for subsequent mixing or processing with other bituminous paving materials. One of the principal advantages resides in the fact that this conditioning may be carried on at the source of supply for the stone, so that it is is unnecessary to have at the point of use the expensive equipment which is now employed where the specifications demand an adequate treatment of the aggregate in order to form a thoroughly satisfactory paving material. The coating on stone which has been conditioned as'noted above fuses effectively with asphaltic cement and the like which is customarily employed, resulting in a better adhesion of the commercial coating to the aggregate than is nowpossible where such coatings are applied directly to the naked and unconditioned stone.

These and further objects of my invention will be set forth in the following specification, reference being had to the accompanying drawing, and the novel means by which said objects are efiectuated will be definitely pointed out in the claims.

The present application is a continuation of my co-pending application for a Method and apparatus for conditioning mineral aggregate, Serial No. 597,164, filed March I, 1932.

In the drawing:

Figure 1 is a diagrammatic, sectional elevation showing the sequential arrangement of the various apparatus units employed in the practice of my improved method.

Fig. 2 is an enlarged sectional elevation of the coating chamber, as this unit appears in Fig. 1.

Fig. 3 is a section along the line 33 in Fig. 2, looking in the direction of the arrows.

Fig. 4 is a diagrammatic, sectional view showing generally the appearance of a piece of aggregate coated according to my improved method.-

Referring to the drawing, the numeral l designates a feeding hopper, the lower end of which is in discharging relationto the lower end of a conveyor H which is denoted as being of the bucket type, although other forms may be employed if desired. The upper end of the conveyor is positioned in discharging relation to one end of a rotary dryer l2 which is generally cylindrical in shape and is mounted for rotation upon the trunnion l3. Rotation of the dryer is effected by means of a pinion M which meshes with a ring gear I 5 that encircles the dryer.

In order to facilitate movement of the aggregate through the dryer, the latter is preferably located in a sloping position with the left, or me.-

terial-receiving end, having the higher elevation. Passage of the aggregate through the dryer is additionally facilitated by the employment of a plurality of spirally arranged blades I6 that project from the inner wall of the dryer, these blades also serving to thoroughly agitate the aggregate during its passage through the dryer, lifting the pieces upwardly and permitting them to fall into the bottom of the dryer in order to insure an intimate contact of the heat which is applied in the manner hereinafter described to thoroughly dry the same.

Extending inwardly from the delivery end i! of the dryer is a casing l8 that may be generically considered as a combustion-chamb er, the inner or left end of the casing, as viewed in Fig. 1, being located at a predetermined distance from the delivery end H for a purpose presently explained. Within the casing [8 may be located a burner l9 which is generally representative of any heat applying means, the hot gases from which are discharged into the dryer through the left end of the casing and are drawn through the dryer by an exhaust fan 20 which is located in an exhaust pipe 2| that communicates with the material-receiving end of the dryer. As illustrated clearly in Fig. 1, the casing l8 defines with the adjacent portion of the dryer l2, an annular space 42 through which is drawn atmospheric air by the fan 20.

From the foregoing. it will be apparent that the mineral aggregate in passing through the dryer will have heat applied thereto until it reaches substantially the inner end of the casing I8, and that from this point until it reaches the delivery end IL'theaggregate will be subjected to the cooling action of fresh atmospheric air which is being drawn through the dryer. It will also be noted that the latter air also serves to remove the moisture that has been expelled from the aggregate by the hot gases flowing from the casing i8.

The delivery end I1 is located in discharging relation to a hopper 22 which in turn feeds the aggregate to the lower end of a conveyor 23 that discharges the aggregate into a storage bin 24. The bin is preferably provided with a sloping bottom 25 that inclines toward the right, as viewed in Fig. 1, the lower end of the bottom defining with the adjacent wall of the bin a discharge opening 26 whose area of opening may be regulated as desired by a gate 21 suitably operated by a lever 28.

The bottom 25 preferably extends within a coating chamber 29 provided with a i'otary distributor 30 that is transversely disposed of the chamber and is mounted in bearings 3| provided therein. The distributor is preferably located immediately below the lower end of the bottom 25 and comprises a cylindrical body 32 from which extends a plurality of radial fins 33. The distributor is appropriately driven in the direction of the arrow 34 (see Fig. 2), so thatas the aggregate is delivered on the distributor from the bin 24, it will be scattered and the pieces thereof momentarily suspended within the coating chamber in the manner generally illustrated in Fig. 2. A plurality of spray nozzles 35 project through the top and side walls of the chamber, these nozzles being externally connected to any suitable source containing a hydrocarbon or bituminous solution and their disposition in the chamber being such as to insure the most effective application of the sprays transmitted thereby at and into the mass of suspended aggregate pieces.

Extending longitudinally of the coating chainber 29 and relatively close to the bottom thereof is a pair of mixing conveyors 36 which are mounted side by side on a pair of shafts 31 that project externally of the chamber for drive by gearing 38. Each of the conveyors is provided with a plurality of radially extending and diagonally disposed blades 39, the blades of one conveyor being preferably arranged in meshing relation with the blades of the other and these conveyors serve the dual function of thoroughly agitating the aggregate pieces which have fallen to the bottom of the chamber in that portion of the solution which may have collected in the same place, and also of gradually moving the collected aggregate toward the delivery openings 40 ofthe chamber for subsequent discharge into a receptacle 4|, noted in this instance as being a railway car.

In conditioning mineral aggregate by the apparatus described above, it is first delivered to the hopper 10, from which it is carried by the conveyor H and discharged into the left end of the dryer )2. Immediately, the aggregate is subjected to an agitating action by the blades it and also to the drying and expanding action of the hot gases flowing from the casing I 8. The agitation of the aggregate insures an intimate contact of the hot gases with each piece there of to the end that all moisture is expelled therefrom, including that held within the pores and interstices of each piece. The pores are substantially enlarged and a large portion of the contained air is also driven out of each piece of the aggregate. It has been ascertained that a temperature of approximately 200 to 300 degrees F..will secure good results in the drying of nor mal types of aggregate, but the stipulation of this range of temperature is not to be considered as restrictive, as this temperature will vary with the type of aggregate being conditioned.

After the gregate has passed the inner end of the casing l8, it immediately becomes subject,

while still being agitated, to the cooling action of atmospheric .air that is being. drawn into the delivery opening I 1 and through the annular passage 42 by the fan 20. This air reduces the temperature of the aggregate to a predetermined extent and the purpose of this cooling will be explained in connection with the treatment of the aggregate in the coating chamber 29.

The slightly cooled aggregate passes into the hopper 22 from which it is ultimately delivered into the storage bin 24 by means of theconveyor 23. The collected aggregate in the bin 24 discharges into the coating chamber 29 where it is immediately scattered and momentarily suspended in the chamber bythe rotary distributor 30. The suspended pieces are subjected to the spraying action of the nozzles 35 which discharge a relatively cool, hydrocarbon solution, such as an' asphalt base oil having preferably an asphalt content of approximately 40 to per cent. I have ascertained that an asphalt solution composed of 55 per cent of 12 to 14 /2 degrees Baum fluxing asphalt, 35 per cent of naptha distillate, 5 per cent of kerosene and 5 per cent of tar naptha to be satisfactory, it being understood that the percentages are approximate in nature. The asphalt content is varied by changing the percentage of the fluxing asphalt in the composition with such changes as may be necessary in the other ingredients. In general, the higher asphalt content would be used with the softer stones, such as limestone, while the lower asphalt content would be used with the harder stones, such as trap rock or granite. Venezuelan, Mexican and Colombian asphalts have been ascertained to be particularly suitable.

Owing to the scattering of the aggregate pieces, it will be obvious that the sprays. will effectually coat the respective surfaces. The sudden applicatiozi of the cool solution to the warmer aggregate pieces which arein a dried and expanded condition obviously results in a rapid chilling of each piece, so that the vehicle portion of the solution is enabled to penetrate deeply within the body of each aggregate piece to substantially water proof the same, this action being facilitated by atmospheric pressure for obvious ireasons, while'the asphalt is also driven into the pores of each piece to form a firm interlock therewith and is further arrested on the surface, thus forming a complete hermetic seal and bonding surface. The solution therefore not only forms a strong mechanical lock with the pores and interstices of each aggregate piece, but it also adheres to the surfaces thereof, with the result that it is characterized by a degree of toughness that is considerably in excess of aggregate which has been treated by any of the standard processes now employed in the industry. As the'material is discharged from the bin 24, it is practically at a temperature that is insufllcient to fractionally distill any of the lighter constituents of the hydrocarbon solution, so that the full properties of the latter are retained in every particular. The temperature of the aggregate as it passes from the bin may be of the order of 125 degrees to 175 degrees F., the former having been found to be a goodworking temperature for the bituminous solution noted above, although these figures may vary somewhat in either direction, dependent upon the nature and condition of the aggregate and the character of the solution employed, while the temperature of the sprayed solution will be the same as atmospheric temperature.

The purpose of the bin 24 is to insure a constant and regulatable discharge of the aggregate into the chamber 29, the gate 21 being operated in relation to a suitable control provided on the nozzle 35 so that the ratio of the solution sprayed into the chamber 29 will be appropriate to the amount of aggregate discharged into the chamber. Excess coating of the aggregate is thereby avoided.

As the aggregate pieces which have been scattered by the distributor 30 fall to the bottom of the chamber 29, they are immediately subjected to further agitation by the mixing conveyors 36 which positively insure a thorough coating of each aggregate piece in that part of the solution which has collected on the bottom of the chamber and also at the same time gradually propels the aggregate toward the discharge opening 40. The precise nature of the aggregate or mixing conveyors 36 forms no part of the present invention, and it will also be understood that a single conveyor of the type illustrated may be employed instead of the twin arrangement shown.

Stone which has been conditioned according to my improved method is characterized by a thin waterproofing and sealing film that is provided by the bituminous solution, this film efiectively preventing at any time thereafter the absorption of any moisture by the aggregate pieces. Since all moisture is expelled from the pores and interstices of the aggregate pieces prior to coating and, further, since the coating positively prevents the reabsorption of moisture by the aggregate pieces, it is readily apparent that the exposure of the aggregate to freezing temperatures thereafter will not cause any peeling of the coating, so that the latter will remain in position for an indefinite time. The nature of the stone is such that it may be stored indefinitely in suitable stock piles without any danger of adjacent pieces becoming unbreakably cemented together, since the extent of the film is insuillcient for this purpose in those sizes of aggregate which are customarily employed for roadway purposes. In other words, the individual pieces, either when stored for a long time or when shipped for considerable distances, will not coalesce together into an agglomerated mass that would require reseparation before the aggregate pieces could be used. Moreover, when aggregate pieces of different sizes are coated according to my improved method and then mixed together to comply with any particular roadway specification and thereafter shipped, the thickness ofthe bituminous film is sumcient to prevent segregation of the aggregate pieces, such as the sifting of the heavier pieces to the bottom of a railway car, for-example. This latter characteristic is quite important as, otherwise, the aggregate mass would require remixing at the point of use in order to insure a thorough and even commingling of the different size pieces of aggregate. Finally, this coating film greatly facilitates the final fusing or merging of the coating on the conditioned aggregate with other paving materials, such as asphaltic cement, when the aggregate is employed in the preparation of a complete paving material.

Insofar as the conditioned aggregate may be shown by drawing, a piece thereof is diagrammatically illustrated in Fig. 4, where the numeral 42 designates a split piece of stone having a ting 43 which extends for some distance into the body of the piece, as represented by the stippling 44. It will be understood that the thickness of the coating in the drawing is considerably greater relative to the size of the piece than would obtain in actual practice, but the drawing does generally illustrate the impregnation and coating of the piece by the solution.

It is contemplated that this method may fulfill a further useful purpose in connection with stone screenings which now constitute a waste product of the quarry. These screenings may be treated by my method in order to provide a material that may be employed as a surfacing for pavements, parking areas and similar locations which are not subjected to the heavy wear of trafilc, such as moves along standard roadways. Under these conditions and when properly rolled down, the coating on these extremely fine pieces will provide an adequate bond with other pieces to form a satisfactory, surfacing layer.

I claim: V

1. The method of treating individual pieces of mineral aggregate to expel the air and moisture therefrom and to provide hydrocarbon hermetic seals therefor whereby to condition the individual pieces for shipment for future use in the fabrication of paving materials, the method comprising the steps of first highly heating the aggregate pieces at a temperature sufiicicnt to evaporate the contained moisture and to expel at least a portion of the air within the interstices of the pieces, then reducing the temperature of the pieces to an extent sufficiently low to prevent substantial vaporization of the volatile constitucuts of the hydrocarbon solution to be subse- 'quently applied, suddenly chilling the dried'and expanded aggregate pieces at their thus reduced temperature by applying a solution of bitumen in a volatile vehicle, the solution having a temperature substantially less than that of the reduced temperature of the aggregate pieces whereby the ensuing contraction of each aggregate piece draws into the body thereof the solution to waterproof the same and to form a thin adherent protective coating of bitumen for each piece to seal the same against the ingress of moisture and to permit the shipment and storing thereof without adherence of the aggregate pieces in mass formation.

2. The method of treating individual pieces of mineral aggregate to expel the air and moisture therefrom and to provide hydrocarbon hermetic seals therefor whereby to condition the individual pieces for shipment and future use in the fabrication of paving material, the method comprising the step of passing the aggregate pieces through a chamber and highly heating the aggregate during a part of its passage to a temperature sufiicient to evaporate the contained moisture and to expel at least a portion of the air within the interstices of the pieces, reducing'the temperature of the pieces during the remainder of their passage through the chamber to an extent sufficiently low to prevent substantial vaporization of the volatile constituents of a hydrocarbon solution to be subsequently applied, and then suddenly chilling the dried and expanded aggregate pieces at their thus reduced temperature by applying a solution of bitumen in a volatile vehicle, the solution having a temperature substantially less than that of the reduced temperature of the aggregate pieces whereby the ensuing contraction of each aggregate piece draws into the body thereof the bituminous solution to waterproof the same and to form a thin adherent protective coating of bitumen for each aggregate piece to seal the same against the ingress of moisture and to permit the shipment and storing thereof without adherence of the aggregate pieces in mass formation.

3. The method of conditioning mineral aggregate to facilitate the subsequent adhesion thereto of bituminous substances to make a complete paving material comprising heating the aggregate pieces to and at a temperature sufficient to evaporate the contained moisture and to expel a portion of the air within the interstices of the pieces, cooling the pieces down to a predetermined temperature and then suddenly chilling the dried and expanded pieces by applying a volatile vehicle and an asphalt combined in solution having a temperature less than that of the aggregate, the reduced temperature of the aggregate being insuificient to vaporize any substantial portion of the solution and the ensuing contraction of each aggregate piece drawing into the body thereof the solution to waterproof the same and form a thin coating of asphalt closely adhering to the surface.

4. The method of conditioning mineral aggregate pieces to facilitate the subsequent adhesion thereto of bituminous substances to make a complete paving material comprising heating and drying the aggregate, delivering the dried aggregate into a chamber, agitating the aggregate during the delivery in a manner to momentarily suspend the aggregate pieces, and then suddenly chilling the dried and expanded aggregate pieces by applying a volatile vehicle and an asphalt combined in a solution having a temperature less than that of the aggregate, the temperature of the heated aggregate being sufliciently low to prevent vaporization of any substantial portion of the solution and the solution being sprayed on the pieces while suspended, the ensuing contraction of each piece drawing into the body thereof the solution to waterproof the same and form a thin coating of asphalt closely adhering to the surface.

5. The method of conditioning mineral aggregate pieces to facilitate the subsequent adhesion thereto of bituminous substances to make a complete paving material comprising heating and. drying the aggregate, delivering the dried aggregate into a chamber, agitating the aggregate during the delivery in a manner to momentarily suspend the aggregate pieces, and then suddenly chilling the dried and expanded aggregate pieces by applying a volatile vehicle and an asphalt combined in a solution having a temperature less 'than that of the aggregate, the temperature of the heated aggregate being sufliciently low to prevent vaporization of any substantial portion of the solution and the solution being sprayed on the pieces while suspended, the ensuing contraction of each piece drawing into the body thereof the solution to waterproof the same and form a thin coating of asphalt closely adhering to the surface, and then further agitating the fallen pieces in that portion of the solution collected on the bottom of the chamber.

6. A device for applying a waterproof coating to mineral aggregate pieces comprising a coating chamber having a supply opening for the aggregate, a rotary agitator having a plurality of radial fins located adjacent the supply opening and adapted to discharge the pieces across the chamber in a condition of momentary suspension, and one or more spray nozzles projecting through the walls of the chamber for applying streams of finely-divided particles of a hydrocarbon solution at and into the mass of suspended pieces to impregnate and coat the same.

7. A device for applying a waterproof coating to mineral aggregate comprising a coating chamber having a supply opening for the aggregate, an agitator located adjacent the supply opening and having means for scattering the ag ate pieces in a state of momentary suspension in the chamber, one or more spray nozzles projecting through the walls of the chamber for applying a hydrocarbon solution to the pieces to impregnate and coat the same, and additional agitating means located in the bottom of the chamber for mixing the fallen pieces in that portion of the solution which has collected on the bottom of the chamber.

8. A device for applying a waterproof coating to mineral aggregate pieces comprising a coating chamber having a supply opening for the aggregate, an agitator adjacent the supply opening having means for scattering the aggregate pieces in a state of momentary suspension in the chamber, and one or more spray nozzles projecting through the walls of the chamber for applying streams of finely divided particles of a hydrocarbon solution at and into the mass of suspended pieces to impregnate and coat the same.

HIRAM M. STAFFORD.

CERTIFICATE OF CORRECTION.

Patent No. 2,041, 155. May 19, 1956.

HIRAM M. STAFFORD.

It is hereby certified that the above numbered patent was erroneously issued to "Sealdrok Company of New England, a corporation of Massachusetts, as assignee by mesne assignments of the entire interest in said invention, whereas said patent should have been issued to the inventor Said "Stafford, sole owner of said invention, as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of September, A. D. 1936.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

